Controlling the aging of xanthates



Patented Dec. 27, 1949 CONTROLLING THE AGING OF XANTHA'EES John .P.Hollihan, J12, Garden City, and. Sanford A. Moss, J12, Ridl'ey 'Park,Pa., assignorsfto American Viscose Corporation, Wilmington,

Del a corporation of Delaware No Drawing. Application August 1 2, 1944,.Serial No. 549,290

4 Claims.

This invention relates to unstable xanthates, such as those of polymericcarbohydrates and particularly of cellulose.

Such xanthates, and especially cellulose. xanthate, as well. astheirsolutions, such as viscose, are unstablev and. tend to hydrolyze sothat xanthate groups gradually break away and are converted intosulfur-containing by-products. As the cellulose xanthate gradually losesits Xanthate groups, .it becomes progressively more insoluble, and thisphenomenon is termed faging? It is common practice to. measure thedegree of solubility by determiningthe concentration of a salt, suchasammonium-chloride or sodium chloride whichwill cause precipitation orgelati'on of the xanthate. Younger or fresher xanthates which have onlypartially .lost their solubility, have higher' salt points. In thefollowing .description', salt point will refer to this index asdetermined with sodium chloride.

In accordance with thispinvention, it has been found that the additionto the cellulose xanthate or a solution thereof of an organic compoundwhich is solubleat least to some extent in the aqueous oralkaline-medium containing the xanthate and having under the conditionsof the xanthate solution a conjugated chain capable of reacting by aprocess of 1:4 addition can reverse the hydrolysis or stabilize thexanthate for extended periods of time; Theexpression process of 1: 4.addition. refers .to the supposed mechanism of the addition type ofreaction of such compounds; in which an intermediate is first formed byaddingv to the carbons or other atoms at the extreme ends of thefour-membered coniugate chain-.. This: reaction mechanismis sometimesreferred to as allylic rearrangement) By Allyl cyanide doesnot contain aconjugated chain, but on introduction into thealkaline solution, thedouble bond-between" the two carbons shifts in a mannersuchthat'aconjugated chain is produced and fi-methyl'acrylonitrile results.

Homologs and other substituted derivatives of the compounds which stillcontain a conjugate chain, capable of 114- addition, orarecapable ofbeing converted into a. compound. having such a conjugated. chain. illithe medium. within which the xanthate is dissolved; may be substitutedfor those specificalIy listeli.

The age-controllingv compounds l or their derivatives mentioned abovewhich are: to be added to the xanthat'e or solution: thereofneedbesoluble only to a sufficient. extent to-permit reaction. However, thosecompounds which: have: cons-id;- erable solubility lend themselves to awider variety and rangev of" application. Preferably, the compoundtome-used should be sufilciently stable so that it will neitherdecompose nor self-polymeri'ze at a.rate. more. rapid than-that at whichit reacts-to producethe salt-point changing effect inthexanthat'e or.solution. Preferably the compound should be completely non-ionizable,though compoundshavinga low degree of ionization may be satisfactory.

in generaL, these age-controllingv compounds have the efiect ofincreasing the salt-point upon addition to the xanthat'e or solution.I-Ioweyer', the particular rate ofincreaseand the time period over whichthis increase will continue with.-

out further addition of the compounds depends using the former.expression. it isnotintended to limit the scope of the claims'tofour-atom chains since: longer chains including a conjugated por tionmay be considered to be merely a shortchain: conjugated. compoundcarrying substituenits on one or both extreme. atoms of" the con-:lugated portion Examples or such compounds which: areihereinaiterreferred: to" as age-controlling. compounds, are as follows:

Acrylonitrile p-Methylacrylonitrlle Acrylamide N-methyl acrylamideN-but'yl acryl'arnide a-Methyl acrylamide N-cyclohexyl acryiami'de'Crotonamide (ii-methyl acrylamide e-Terpinene fl-Terpinene (A3319)hadiene Allyl cyanide upon the particular compound. For. example,acryl'onitrile when added in the amountlof 2% on the viscose raises thesalt-point from 4.5 to 12 within a period" of ten minutes, whereas allylcyanide in the. same amount causes a change from 14.5 to. 12" salt-pointin twenty-four hours. In all cases the addition of a given. amount ofone of these compounds-causesarise. in the saltpoint up, to amaximum,gwhi'ch. maximum depends upon the particular compound. and theamount in. which it is added',, after which the xanthate or solutionagainproeeeds through an aging process, theirate of; which depends uponthe particular compound, some causing more rapid. and others causingarslower rate of aging than. that of any standard. viscose solution ofthesame salt-point- (that is, one having. the maximum salt-pointreached. upon addition. of the compound) under the same conditions. Asstated above, the rate at which the rise occurs and the maximum riseobtainabledepend upon each individualcompound. Byselecting a com poundwhich eiiectsa relatively-small. increase in salt-point (that is. onewhich has, a relatively low maximum) and which is relatively slow bothin producing this rise and in subsequent reaging, the eifect is to causestabilization of the xanthate or solution for a period of time extendingfrom the point of addition through the maximum to the subsequent timewhen hydrolysis after reaching the maximum again returns the viscose toits original salt-point. For example, the addition of 2% of iii-methylacrylamide to viscose having a salt-point of 5 raised the point to 6.9in 5 hours and the salt-point did not thereafter fall below 6.9 until 18to 24 hours later.

While it is not desired to be limited to any particular theory ofoperation, it is thought that the compounds react with thesulfur-containing by-proclucts which are produced upon hydrolysis of thexanthate, such as sodium trithiocarbonate, sodium sulfide and sodiumhydrosulfide to produce carbon disulfide, and the development of thiscompound apparently elfects further xanthation of the sodium celluloseor of the partially hydrolyzed cellulose xanthate. When acrylonitrile isused, the reactions seem to pro ceed as follows (disregarding thereaction of the acrylonitrile directly with the viscose):

In the above series of equations, the insolubility of the CNC2H4SC2H4CN(underlined in the equation above) apparently causes a shift ofequilibrium which produces the carbon disulfide and sodium hydroxide (indouble parentheses) in the third and fourth equations. The increase inconcentration of carbon disulfide apparently causes a reversal of thefirst equation above in the manner represented by the last equation.

The effect of these age-controlling compounds on cellulose xanthate orsolutions thereof, particularly the viscose solutions which find use forspinning filaments, for the production of films or sheets of cellophane,or for the production of plastic masses in general, may be used invarious ways to adjust the age of the viscose. For example, one of thesecompounds in the desired amount may be added to the Viscose after it hasripened to the proper extent for spinning purposes. By incorporating oneof the compounds which has a slow rate of action, and which does notincrease the salt-point to such an extent as to throw the viscose into astage of ripening outside the range of spinnability under the conditionsemployed, a virtual stabilization is eifected for that interval which isrequired for the viscose to go to a maximum salt-point and return to itsoriginal salt-point. Besides stabilizing during the period of spinningfrom a single tank of the spinning solution, a great improvement isnoted in the compatibility of the heel of solution leftin a given tankand the next batch of solution introduced therein. The incorporation ofthese compounds also serves to facilitate the control of the agingprocess in that it serves to minimize the variations in the salt.- pointcaused by fluctuation in the conditions of storage. When pigments,delustrants, or other materials are to be mixed into the viscose, asmall proportion of one of these age-controlling compounds may be addedsimultaneously to minimize the sensitivity of the aged viscose to themechanical agitation necessitated by the mixing.

The amount of the age-controlling compound introduced in the viscose mayvary considerably depending upon the particular effect desired. Amountsranging from as low as about 0.1% to as much as 10% or more based on theviscose may be introduced at any one time. If desired, additionalamounts may be introduced at regular intervals after the effect of thepreceding addition has worn 01f. Such additions may be made repeatedlyto rejuvenate an aged viscose. However, it is desirable to add sodiumhydroxide in conjunction with the compounds when additions subsequent tothe first or second are made. If desired, the age-controlling compoundsmay be used in conjunction with the conventional ageinhibitingcompounds, such as sodium sulfites.

While preferred embodiments of the invention have been disclosed, it isto be understood that changes and variations may be made withoutdeparting from the spirit and scope of the invention as defined by theappended claims.

We claim:

1. The process of adjusting the age of alkaline cellulose xanthates andsolutions thereof comprising the step of incorporating therein acompound selected from the group consisting of acrylonitrile.,B-methylacrylonitrile, acrylamide, N-methyl acrylamide, N-butylacrylamide, ormethyl acrylamide, N-cyclohexyl acrylamide, c-methylacrylamide, and allyl cyanide.

2. The process of adjusting the age of alkaline cellulose xanthates andsolutions thereof comprising the step of incorporating acrylonitriletherein.

3. The process of adjusting the age of alkaline cellulose xanthates andsolutions thereof comprising the step of incorporating a-methylacrylamide therein.

4. The process of adjusting the age of alkaline cellulose xanthates andsolutions thereof comprising the step of incorporating fi-methylacrylamide therein.

JOHN P. HOLLIHAN, J R. SANFORD A. MOSS, JR.

REFERENCES orrsn The following references are of record in the file ofthis patent:

(Copy in Scientific Library, Patent Office, Washington. D. C.)

